scholarly journals Ab-initio density-functional lattice-dynamics studies of ice

2003 ◽  
Vol 81 (1-2) ◽  
pp. 115-122 ◽  
Author(s):  
A S Cote ◽  
I Morrison ◽  
X Cui ◽  
S Jenkins ◽  
D K Ross
Keyword(s):  
Ab Initio ◽  
Force Constant ◽  
Density Functional ◽  
Phonon Dispersion ◽  
Scattering Data ◽  
Full Potential ◽  
Dynamical Matrix ◽  
Constant Matrix ◽  
Force Constant Matrix ◽  
Dynamical Properties

We present the results of first-principles computational studies of the dynamical properties of hexagonal ice using both the ab-initio pseudopotential method and the full-potential augmented plane-wave method. Properties obtained using both the generalized gradient approximation (GGA) and the meta-GGA in density-functional theory are compared. The lattice-dynamical properties of the structures are obtained using a finite-difference evaluation of the dynamical matrix and force-constant matrix from atomic forces. Phonon dispersion is evaluated by the direct determination of the force-constant matrix in supercells derived from the primitive molecule unit cells with the assumption that force constants are zero beyond the second molecular nearest neighbors. The k-dependent phonon frequencies are then obtained from the force-constant matrix and dispersion relations, and the Brillouin-zone integrated density of states is evaluated. The importance of phonon dispersion in the various regions of the phonon spectra is then assessed and compared to existing neutron-scattering data. Frozen-phonon calculations are used to compare phonon frequencies evaluated in both the GGA and meta-GGA. PACS Nos.: 61.12Ex, 63.20Dj

Electronic Structure Of (AgSb)xPbn-2xTen

2003 ◽  
Vol 793 ◽  
Author(s):  
Daniel I Bilc ◽  
S.D. Mahanti ◽  
M.G. Kanatzidis
Keyword(s):  
Electronic Structure ◽  
Ab Initio ◽  
Density Functional ◽  
Full Potential ◽  
Generalized Gradient ◽  
Two Component System ◽  
Functional Theory ◽  
Covalent Interaction ◽  
Salt Structure ◽  
Linearized Augmented Plane Wave

ABSTRACTComplex quaternary chalcogenides (AgSb)xPbn-2xTen (0<x<n/2) are thought to be narrow band-gap semiconductors which are very good candidates for room and high temperature thermoelectric applications. These systems form in the rock-salt structure similar to the well known two component system PbTe (x=0). In these systems Ag and Sb occupy Pb sites randomly although there is some evidence of short-range order. To gain insights into the electronic structure of these compounds, we have performed electronic structure calculations in AgSbTe2 (x=n/2). These calculations were carried out within ab initio density functional theory (DFT) using full potential linearized augmented plane wave (LAPW) method. The generalized gradient approximation (GGA) was used to treat the exchange and correlation potential. Spinorbit interaction (SOI) was incorporated using a second variational procedure. Since it is difficult to treat disorder in ab initio calculations, we have used several ordered structures for AgSbTe2. All these structures show semimetallic behavior with a pseudogap near the Fermi energy. Te and Sb p orbitals, which are close in energy, hybridize rather strongly indicating a covalent interaction between Te and Sb atoms.

scholarly journals Magnetic Properties and the Electronic Structure of the Gd0.4Tb0.6Co2 Compound

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5481
Author(s):  
Marcin Sikora ◽  
Anna Bajorek ◽  
Artur Chrobak ◽  
Józef Deniszczyk ◽  
Grzegorz Ziółkowski ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Photoelectron Spectroscopy ◽  
Density Functional ◽  
Magnetic Measurements ◽  
Plane Waves ◽  
Full Potential ◽  
Theory Approach ◽  
Xps Spectra

We report on the comprehensive experimental and theoretical studies of magnetic and electronic structural properties of the Gd0.4Tb0.6Co2 compound crystallization in the cubic Laves phase (C15). We present new results and compare them to those reported earlier. The magnetic study was completed with electronic structure investigations. Based on magnetic isotherms, magnetic entropy change (ΔSM) was determined for many values of the magnetic field change (Δμ0H), which varied from 0.1 to 7 T. In each case, the ΔSM had a maximum around room temperature. The analysis of Arrott plots supplemented by a study of temperature dependency of Landau coefficients revealed that the compound undergoes a magnetic phase transition of the second type. From the M(T) dependency, the exchange integrals between rare-earth R-R (JRR), R-Co (JRCo), and Co-Co (JCoCo) atoms were evaluated within the mean-field theory approach. The electronic structure was determined using the X-ray photoelectron spectroscopy (XPS) method as well as by calculations using the density functional theory (DFT) based Full Potential Linearized Augmented Plane Waves (FP-LAPW) method. The comparison of results of ab initio calculations with the experimental data indicates that near TC the XPS spectrum collects excitations of electrons from Co3d states with different values of exchange splitting. The values of the magnetic moment on Co atoms determined from magnetic measurements, estimated from the XPS spectra, and results from ab initio calculations are quantitatively consistent.

Synthesis process, magnetic and electronic properties of ferrite nanoparticle MnFe2O4

2018 ◽  
Vol 14 (4) ◽  
pp. 663-675
Author(s):  
R. Masrour ◽  
M. Ben Ali ◽  
H. El Moussaoui ◽  
Mohamed Hamedoun ◽  
A. Benyoussef ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Ab Initio ◽  
Density Functional ◽  
Synthesis Process ◽  
Physical Parameters ◽  
Full Potential ◽  
Theory Approach ◽  
Content Type ◽  
Electronic And Magnetic Properties ◽  
Ferrite Nanoparticle

Purpose The purpose of this paper is to synthesize the manganese ferrite nanoparticle MnFe2O4 and to investigate the structure, size and to study the electronic and the magnetic properties of MnFe2O4 nanoparticles. Design/methodology/approach The co-precipitation method is used to synthesize the MnFe2O4. The structure and size were investigated by X-ray diffraction. The superconducting quantum interference device is used to determine the some magnetic ground. From theoretical investigation point of view self-consistent ab initio calculations, based on density functional theory approach using full potential linear augmented plane wave method, were performed to investigate both electronic and magnetic properties of the MnFe2O4. The high temperatures series expansion (HTSE) is used to study the magnetic properties of MnFe2O4. Findings The saturation magnetization, the coercivity and the transition temperature varied between 21-43 emu/g, 20-50 Oe and 571-630 K, respectively, have been studied. The gap energy of MnFe2O4 has been deduced. The critical temperature and the critical exponent have been obtained using HTSEs. Originality/value In the present work, the authors study the electronic and magnetic properties of MnFe2O4. The results obtained by the experiment and by ab initio calculations were used in HTSE as input to deduce other physical parameters.

scholarly journals Ab initio studies of structural, electronic, optical, elastic and thermal properties of CuGaTe-=SUB=-2-=/SUB=-

2017 ◽  
Vol 51 (5) ◽  
pp. 711
Author(s):  
Pravesh Singh ◽  
Sheetal Sharma ◽  
Sarita Kumari ◽  
Vibhav K Saraswat ◽  
D. Sharma ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Ab Initio ◽  
Density Functional ◽  
Structural Parameters ◽  
Debye Model ◽  
Full Potential ◽  
Augmented Plane Wave ◽  
Different Temperatures ◽  
First Time ◽  
Linearized Augmented Plane Wave

We have performed ab initio calculations for the structural, electronic, optical, elastic and thermal properties of CuGaTe2. In this study, we used an accurate full potential linearized augmented plane wave (FP-LAPW) method to find the equilibrium structural parameters and to compute the full elastic tensors. We report electronic and optical properties with the recently developed density functional of Tran and Blaha. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, were calculated for photon energies up to 30 eV. The thermodynamical properties such as Debye temperature, entropy and Gruneisen parameter, bulk modulus and hardness were calculated employing the quasi-harmonic Debye model at different temperatures (0-1000 K) and pressures (0-8 GPa) and the silent results were interpreted. Most of the investigated parameters are reported for the first time. DOI: 10.21883/FTP.2017.05.44433.8044

Ab Initio Calculations on the Structural, Mechanical, Electronic, Dynamic, and Optical Properties of Semiconductor Half-Heusler Compound ZrPdSn

2016 ◽  
Vol 71 (2) ◽  
pp. 135-143
Author(s):  
Yasemin Ö. Çiftci ◽  
Cansu Çoban
Keyword(s):  
Optical Properties ◽  
Ab Initio Calculations ◽  
Bulk Modulus ◽  
Ab Initio ◽  
Density Functional ◽  
Phonon Dispersion ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Reflectivity Function ◽  
Murnaghan Equation

AbstractThe structural, mechanical, electronic, dynamic, and optical properties of the ZrPdSn compound crystallising into the MgAgAs structure are investigated by the ab initio calculations based on the density functional theory. The lattice constant, bulk modulus, and first derivative of bulk modulus were obtained by fitting the calculated total energy-atomic volume results to the Murnaghan equation of state. These results were compared to the previous data. The band structure and corresponding density of states (DOS) were also calculated and discussed. The elastic properties were calculated by using the stress-strain method, which shows that the MgAgAs phase of this compound is mechanically stable. The presented phonon dispersion curves and one-phonon DOS confirms that this compound is dynamically stable. In addition, the heat capacity, entropy, and free energy of ZrPdSn were calculated by using the phonon frequencies. Finally, the optical properties, such as dielectric function, reflectivity function, extinction coefficient, refractive index, and energy loss spectrum, were obtained under different pressures.

The effects on the lattice dynamical properties of the temperature and pressure in random NiPd alloy

2013 ◽  
Vol 91 (10) ◽  
pp. 833-838 ◽  
Author(s):  
S. Kazanc
Keyword(s):  
Phonon Dispersion ◽  
Alloy System ◽  
External Pressure ◽  
Dynamics Simulation ◽  
Dynamical Matrix ◽  
High Symmetry ◽  
Embedded Atom ◽  
Dynamical Properties ◽  
Temperature And Pressure ◽  
Many Body Interactions

In this work, the effects on the lattice dynamical properties, such as phonon dispersion, second order elastic constants, and bulk modulus of the temperature and pressure in random NiPd binary alloy system was investigated using molecular dynamics simulation. The interactions between atoms were modelled using the Sutton–Chen-type embedded atom method based on many-body interactions. The phonon frequencies were calculated from the dynamical matrix for [100], [110], and [111] high symmetry directions of the Brillouin zone. The obtained results show that the external pressure cause an increment in phonon frequencies, and the increase of temperature causes a decrease in longitudinal and transverse acoustic phonon frequencies because of thermal expansion.

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